For example, a chain saw, which is a type of portable power work machine, normally includes a machine body portion housing a power source such as an engine or an electric motor, a power transmission mechanism, and the like; a cover attached to cover a predetermined region of the machine body portion (such as the power transmission mechanism portion including a drive sprocket); a guide bar held between the machine body portion and the cover and having a saw chain extended around the guide bar; bolts passed through an elongated hole or an elongated groove provided in the guide bar and through insertion holes provided in the cover, the bolts being securely embedded in the machine body portion; and fastening nuts threadably engaged with the bolts so as to compressively hold the guide bar between the machine body portion and the cover.
During the use of the chain saw, the saw chain may become elongated by heat, becoming loose. Thus, the saw chain needs to be re-tensioned from time to time. Also, when the saw chain or the guide bar is replaced, the tension of the saw chain needs to be adjusted after the saw chain is extended around the drive sprocket and the guide bar.
In order to adjust the tension of the saw chain, replace the guide bar, or maintain and check sliding portions, for example, it may become necessary to detach the cover from the machine body portion, requiring loosening the nuts and removing them from the bolts.
Once removed from the bolts, the nuts are separate from the machine body portion or the cover. Thus, the nuts may be easily lost, particularly during a logging operation in the mountains, for example. If the nuts are lost, the cover cannot be attached to the machine body portion, making it impossible to compressively hold the guide bar between the machine body portion and the cover.
Conventionally, structures for preventing the falling of the fastening nuts have been proposed, as described in Patent Documents 1 and 2, for example.
The structure for preventing the falling of the fastening nuts described in Patent Document 1 includes a nut anchor member for anchoring the nuts to the cover. The nut anchor member includes a circular portion externally held on a lower outer periphery of the nut by swaging; three downwardly extending leg-like piece portions extending downward from the circular portion; and bifurcated locking nail portions provided at the lower end of the leg-like piece portions. The cover is provided with associated locking holes for locking the bifurcated locking nail portions so as to prevent the nut and the nut anchor member from falling from the cover when the nut is detached from the bolt.
The structure for preventing the falling of the fastening nuts described in Patent Document 2 also includes a nut anchor member for anchoring the nut to the cover. The nut anchor member comprises an elastically deformable sheet or thin plate with its respective parts lying in a common plane, and includes a circular or split-circular externally fitting portion which is externally fitted into a circular groove portion provided at the lower outer periphery of the nut. The externally fitting portion is continuous with a U-shaped leg portion which is in turn continuous with a proximal end portion that is affixed to the cover with a screw.